Recently, Bicycle Quarterly’s experiments on suspension losses have been replicated and confirmed: Higher tire pressures don’t result in faster speeds – even on smooth pavement. Replicating results is a crucial part of science, which makes the new results an important milestone in the understanding of bicycle performance. No longer is it just Bicycle Quarterly talking about suspension losses and lower tire pressures – the science is becoming widely accepted.

When Bicycle Quarterly’s tire tests (below) showed that higher pressure didn’t make your tires faster, few people believed it. Back in 2007, everybody “knew” that pumping up your tires harder made them faster.

We had doubts, too. So we tested again and again, and our results always were the same. We concluded that it was true, even if it went against the accepted wisdom of almost 100 years of cycling knowledge.

Looking through the literature and talking to experts like Jim Papadopoulos, we found a mechanism that could explain this: suspension losses caused by vibrations. As the tissues in the rider’s body rub against each other, friction turns energy into heat. And that energy must come from somewhere: It is taken from the forward momentum of the bike. Your body vibrates, and that slows down the bike. (The bike also vibrates, but it’s not as significant, since it’s mostly made from hard materials that don’t generate much friction.)

The next step was to prove that these vibrations could cost significant power. We went to rumble strips on the shoulder of a highway (photo at the top), because they allowed side-by-side comparison between smooth pavement and a “standardized” rough surface. The results were surprising: Riding on the rough surface took up to 290 Watts more than riding on the smooth surface (below).

Where did those 290 Watts go? After testing various pieces of equipment on the rumble strips all day, I knew where the energy went: My body was sore all over. I had experienced suspension losses on my own body!

Careful testing is only a first step. Real science demands that all scientific experiments are repeatable and replicable.

Repeatable means that if you run the same experiment twice, you must get the same result. We did that multiple times: Each configuration was run at least three times. And we ran the same equipment at the beginning, in the middle and at the end of the test, to make sure that conditions (wind, temperature, etc.) did not change and affect the results.

Replicable means that others must be able to do the same experiment, and get the same results. We published our methodology for testing suspension losses in Bicycle Quarterly. That was back in 2009, and we’ve been waiting for others to replicate them. We are excited that now Joshua Poertner has done similar test, also using rumble strips. And his results are similar to ours:

The blue line at the bottom shows the old-style steel drum tests: Higher pressure makes your tires faster. But that is true only if you don’t have a rider on board. (No rider = few suspension losses)

Once you put a rider on the bike, things start to look very different: The green line shows brand-new asphalt, the yellow line coarse intermediate asphalt, and the red line are the rumble strips. You can see that resistance increases beyond a certain pressure. This is the opposite of the old wisdom, which is expressed by the blue line.

It’s important to remember that the green, yellow and red lines are real-world testing. The blue line is done in the laboratory. And when laboratory tests don’t match the real world, then they are useless.

The article doesn’t mention Joshua Poertner’s methodology. I am a bit surprised that the dropoff in performance at higher pressures is so large. Our own testing (above) – on very smooth pavement – showed that very high pressures actually resulted in the same performance as lower pressures – not worse performance, as Joshua Poertner’s data seem to indicate. In the future, we’ll have to figure out which is correct. Or perhaps it’s a simple matter of Joshua Poertner’s “smooth” asphalt being rougher than ours…

However, everybody now agrees that higher pressures do not make you faster. We also agree that when things get rough, higher pressures are actually slower.

For riders, what matters most is how you can make your bike faster. And Joshua Poertner’s advice mirrors what we’ve been saying for years: “It turns out that it’s much better to be 10 or even 20 psi lower than the ideal tire pressure than 10 psi higher.” And: “Here’s the next thing you have to think about. As tire width increases, tire pressure decreases. So a wider tire performs better in terms of rolling performance.”

Looking into the future, Poertner said: “I remember when wheels went from 19 mm to 23 mm. It was a very gradual process. And then we went from 23 mm to 25 mm. Now we’re seeing 28 mm wheels. Where does it stop? I don’t know.”

And we all agree that wider tires are faster because they can run at lower pressures over a mix of surfaces. Joshua Poertner is comparing identical tires at different widths. It is understood that to offer good performance, the wider tires must be supple, otherwise, you lose too much energy to flexing the tire casing at it deforms with each wheel revolution.

In other words: On most roads, and especially on rough ones, a 32 mm Compass tire will be faster than a 26 mm Compass tire. But a 42 mm Schwalbe Marathon will be slower than both, even though it’s wider – because it’s so stiff that its casing absorbs way more energy.

Here is what it means in practical terms:

Run the widest tire that fits your frame, at least within reason. Bicycle Quarterly’s tests have shown that 32 mm tires roll as fast as 25 mm even on very smooth asphalt, and faster than 23 mm or 20 mm. On rough roads, the wider tires are clearly faster. Since we measured this at 22 mph (35 km/h) with a rider, this takes into account the wind resistance at typical “spirited” cycling speeds.

Run your tires at a relatively low pressure that still offers good handling. You don’t want your tires collapse under hard cornering, but beyond that, there is no benefit to adding more air. Experiment with different pressures, but don’t be afraid to let out some air.

Select the most supple tire for the best performance.

It’s taken almost a decade, but it’s nice that our results finally have been replicated and confirmed. What once was controversial is becoming universally accepted. And as Joshua Poertner points out (“Where does it stop?”), there is more research to be done. Fortunately, Bicycle Quarterly is already working on this!

80 Responses to Suspension Losses Confirmed

Nice timing for your post. In the last weeks I tried to decrease the pressure in my 650Bx42mm Grand Bois Hetres down to the point where I’m afraid my front tire could jump out of the rim in strong cornerings. My Silca pump said it is a bit below 2 bars (But I’ve never checked the exactitude of it). It feels great, and riding alone I couldn’t tell anything about the performance so I just enjoyed the plush comfort. But at the end of my last ride I ended up riding with a friend and I realised he was going much faster than me, even when not pedalling. I did increase the pressure and it seemed to get a bit better. At this point we’re quite in the anecdotical territory but I learned from this experience that there might be a thing as not enough pressure, even for a loyal BQ reader🙂

The best way to compare bike performance with a friend whose bike seems faster is to switch bikes. If he coasts faster on your bike, then he’s just heavier/shorter/more aero. If you coast faster on his bike, then your bike really is slower.

Interesting stuff, however I think it may take some time before “received wisdom” changes as in my anecdotal experience, many club cyclists think they should keep tyres pumped up too high and wider tyres are still viewed with suspicion…

Are there any objective measurements of suppleness? So for example, same tyre width, same pressure then put on a known load and measure the tyre deflection, is this a measure of suppleness?

“Objective” measures of suppleness are difficult to establish, but your idea of measuring the deflection under a given load is a first approximation. Frank Berto did this in the 1980s, when he measured tire drop. The more supple tires had much more tire drop than the stiffer ones. It won’t be truly an accurate measure of suppleness, because you need the dynamic, not static, deflection as the wheel rotates.

You’ve probably had a flat and not noticed, so you will be familiar with the feeling of the tire collapsing under cornering loads. It’s scary, but you are unlikely to crash.

The best approach is to go in small steps. So when the handling starts getting weird – and by that I don’t mean that the tire doesn’t feel like a rock anymore, but truly deflects when you corner or climb up cambers in the road surface – then add a little air and see whether the weird feeling goes away.

Stand up and sprint HARD. Watch and “feel” your front tire. If it’s too hard, you won’t see much give. If it’s too soft you’ll see and feel it collapsing. I like my tires just soft enough that my hardest sprinting deforms them significantly, but not to the edge of collapsing. It’s a fairly wide range. Then set the rear a bit firmer than the front.

In thinking about the net impacts of wider tires, I’m wondering whether there is a negative in terms of the energy needed for acceleration? The tires are heavier and it seems like this might result in more energy expenditure when speeding up? Also, would you expect any significant aerodynamic effects? I guess it’s probably difficult to test, but wouldn’t we ideally want some measure of the net impacts of wider tires across an entire ride (or across different types of rides, e.g., steep, flat, etc.?

When you look at the physics, you realize that wheel weight isn’t that important for acceleration. In simple terms, cyclists don’t accelerate very quickly… A pro cyclist has only 1/10 the power-to-weight ratio of the smallest economy car! If wheel weight was as important as most cyclists think, then all pro racers would use the smallest (and thus lightest) wheels that are UCI-legal. The fact that they still ride 700C wheels – despite many experiments with smaller wheels – shows that it cannot make a big difference even at the pro level.

Where wheel weight matters is when you throw the bike from side to side in a sprint. There, your lateral accelerations are quite large, and a bike with heavier wheels will feel different. The solution is going to smaller wheels as tire width increases. That is why we like 650B wheels for tires wider than 35 mm, and 26″ wheels for tires wider than 45 mm.

As to testing under a wide range of conditions, that would be interesting, but as you say, very difficult. And the physics indicate that there wouldn’t be much difference. Our on-the-road experience matches this: We have a bunch of well-matched riders, and if the rider on the wider tires was slower, we’d notice. So far, they aren’t slower.

Conventional wisdom actually says that wheel weight is super-important. However, the laws of physics say otherwise. And the pros who’ve tried smaller and lighter wheels also don’t seem to have found them faster. So while there is more testing that could be done – see the comment about micro-accelerations – it’s hard to conclude that lighter wheels really make the bike significantly faster.

Here’s my experience. I’ve got a disc brake any-road type bike, and have two sets of wheels. One with alloy rims and Compass Bon Jons that I use at about 40-45psi, the tires measure ~37mm on my rims. The other is a set of 36mm deep carbon wheels with Schwalbe One tubeless tires, “23mm” tires that measure over 26mm on my rims, used at 75-80psi. The carbon/skinny set is about 0.4lbs lighter.

When venturing off pavement, obviously, the wider tires are best – that’s why I’ve got them! When riding pavement, riding solo and not in a big hurry (14-15mph average), either set works fine, the big tires don’t feel like they hold me back any.

But, jump into a group ride where the speeds are higher (20+mph average speeds) the narrower tires are noticeably faster. I’m betting it’s the better aerodynamics, not lower weight or any difference in rolling resistance. They hold their speed better, require less effort to close gaps, and let you coast a bit more when holding someones wheel. It’s a lot easier to stay with the group with the more aerodynamic wheel/tire combo.

The big tires work over a wider variety of surfaces/conditions, and they’re more comfortable. But when speed is the goal, and pavement is the surface, the skinnier tires are faster.

Dustin, you raise some interesting points. I find some of your observations hard to square with the laws of physics. You say that the lighter wheels hold their speed better – I would expect the added rotational inertia of a heavier tire/wheel combo to hold its speed better (at least marginally). Less effort to close gaps could make sense (again marginally so). Coast a bit more when holding someone’s wheel – again, that effect would be very hard to measure, since you are probably riding behind different riders, in different wind conditions, etc.

It would be good to see power data – for example, you riding behind the same rider, same temperature and same no-wind condition, with one wheelset and then the other. Then we’d have something to compare.

That’s similar to my experience. i ride Panaracer 35s and when my group is riding their fat tires, I’m king but when we hit the smooth pavement and they switch their bikes to the skinny racers (I don’t have one), I’m choking on their dust. Caveat here is that they’re using completely different bikes.

I think what you are experiencing is more the flex characteristics of the frame. When I tested a Surly Long-Haul Trucker for Bicycle Quarterly, even with supple 32 mm tires, I had a hard time keeping up with my friend on his randonneur bike, despite his bike running 42 mm tires. Clearly, it wasn’t the tires, nor the weight (the Surly without fenders, lights and racks wasn’t much heavier than the fully equipped randonneur bike), but the flex characteristics of the frame.

In my case, since I’m riding the same bike, it’s not frame flex. It’s aerodynamics. When you’re doing 25-30mph aero drag is the biggest thing holding you back, not rolling resistance or bearing drag or anything else. The skinnier tires, with deeper wheels, are noticeably faster when really hammering along, or I should say, they’re noticeably easier to maintain speed when hammering along. My experience matches the sensations people explain when they switch their road racing bike’s wheels from traditional box section rims to deeper more aerodynamic rims – you can more easily ‘surf the peloton’ as one person put it.

I have discovered that low tire pressure results in a sluggish feeling when climbing a smooth road out of the saddle. In this circumstance, low tire pressure subjectively feels slow. Can you confirm my experience? Perhaps this is a situation when too much casing deflection results in a loss of speed?

It probably depends on the tires. I know the feeling of the tire deflecting a lot as you ride out of the saddle, and you do flex the casing more. In my experience, the speed loss doesn’t seem noticeable (riding next to cyclists of equal strength who climb at my speed), but I use supple tires. With stiffer tires, it might make more of a difference.

In any case, unless you ride on gravel, you could increase your tire pressure a bit, and the feeling will go away.

Years ago, I spent one or two seasons riding a fully-suspended Moulton AM-7. One of the drawbacks of the front suspension was that climbing out of the saddle felt unproductive. I spent more time bouncing the forks up and down like a pogo stick than I did driving the bike forward. This explained to me the need to lock out the front suspension on mountain bike forks. I’ve been reluctant to go to much wider tires and lower pressures for this reason; I think the same thing may be happening here. At the very least, I normally pump my tires to “worst case,” which means equal pressure front and rear. This addresses the dynamic nature of weight distribution on a bike. when you’re out of the saddle, front/rear weight distribution goes from 40/60 to 60/40, or even 70/30. The weight shift is even more dramatic under braking.

The effect you mention is real. It’s unpleasant, and it probably slows you down. That is one reason why I prefer 42 mm-wide tires on the road over 54 mm. And I don’t like sprinting with gravel pressures. But below 42 mm and with road pressures, I don’t get it even when sprinting hard. And as a former Cat. 2 racer, sprinting hard means pushing the bike to its limits.

In fact, in a sprint, very high pressures have the rear wheel hopping around and not able to transmit power on all but the smoothest surfaces. With wider tires at somewhat lower pressures, you don’t get that. So like everything, it’s not that the lowest possible pressure is best. It should be just right, considering the factors involved.

I have a tandem that will only fit a 32mm tire.
Given the extra weight of the bike and second rider, will super supple tires still be a benefit or is there a point where a bit sturdier casing becomes necessary?

Speaking of tire pressure, I’ve had a set of the Rat Trap Pass tires for a while, and have been curious about what pressures I should be using in them. Running them at 45 psi resulted in glass shards causing punctures.

I’ve been running some Schwalbe Marathon Almotion tires at 30-35 psi without any weird handling problems, and with great comfort both on and off pavement, and not much slowdown. Would that not be too low for the Rat Trap Pass?

What is mostly schocking about the whole research on rolling resistance is not the technical but social/psychological aspect.
It’s hard to believe how many regular riders, professional teams, jurnos could be wrong about performance differences that could be often dected with a simple stopwatch.
We live in the age of powermeters, £300 glorified gps cycle computers, Strava, and yet so few has noticed that changes in tyre width and pressure have most often the opposite effect to what they believe it should have had.
I’m pretty certain sociology defines this phenomenen more elegantly than a… collective brainwash, or herd mentality…?

Anyway…
I’ve been rolling on 25mm and 28mm (27mm and 31mm actual widths) Schwalbe One tubeless tyres. I started from 80PSI and ended at no more than 60 front and 70 rear. Will be trying 50 and 60 as long as handling and rim strikes don’t become an issue.

That’s an interesting observation. I think there are two factors at play:

1. We don’t usually question things “everybody knows”. For more than 1000 years, it was accepted that the earth was flat, despite evidence to the contrary.

2. More importantly, higher pressures really do feel faster, since the frequency of the road vibrations increases in the same way as it does when you ride faster. In other words, higher pressures give you the sensation of going faster – without actually going faster.

I think between these two, it’s easy to explain why generations of cyclists thought that pumping your tires up harder made you faster. You knew it, and you could feel it!

We discovered that higher pressures are not faster almost by accident, too. We wanted to see how much faster higher pressures really were. To our surprise, as we increased the pressure, we didn’t get faster at all. At first, it was hard to believe, but we checked different tires multiple times, with two different methodologies (roll-down and power meter), and the results were the same.

“wheel weight isn’t that important for acceleration”. Well, yes it is. Even more important
(for our purposes) is where on the wheel that the weight is located. Weight of the tyre increases moment of inertia, which makes the wheel (and bike) slower to accelerate with a given power input. A smaller wheel must rotate faster for the same road speed, increasing bearing friction, rolling resistance, windage, and inertia losses. A larger wheel would have less of all four types of losses.
.
A bit more on inertia losses; pedalling a bike is a non-linear process, despite claims that
clipless pedals allow a 360 degree constant force to be applied. Actual tests with force-transducers indicate otherwise. That being the case, pulsating accelerations are taking place and inertia losses become significant. I would have to run some numbers to determine whether the reduced weight of a smaller wheel would have a greater effect on inertia losses than the increased rotational speed required.
.
Moment of inertia increases with a given weight located farther from the center of rotation (axle)
AND/OR with an increase in weight for a given distance from the center. In our case, we must work with a constant wheel radius and variable weight for moment of inertia considerations. I have noticed dramatic differences in performance when switching to a lighter wheel or tyre.

You are right that all these factors matter, but the question is “How much”. As a ridiculous example, getting a haircut before a race will make you lighter, but it probably won’t be enough to affect the race results.

So on to smaller wheels: Bearing resistance is almost zero, so the faster spinning wheel still will be almost zero. Rolling resistance isn’t affected by wheel diameter. We’ve measured this – the angle of attack simply isn’t that different between 26″, 650B and 700C. Wind resistance – conventional wisdom says that the smaller wheel should be more aero. The same for inertia. So overall, the smaller wheel should come out way ahead.

I think the micro-accelerations you mention could be important. At first sight, one might think that it might be desirable to keep the bike at constant speed – hence heavier wheels – but it’s like what we call “planing”: If you can put in more power on the downstroke because the bike gives (either by flexing its frame or by accelerating the entire bike), then you can put out more power, compared to a bike that “resists” your pedal strokes. So perhaps light wheels are more important on stiffer bikes that don’t “plane”?

Overall, you have to do the math to find out how little wheel weight matters in acceleration. I did that years ago. The difference between a superlight wheelset (sub-300 gram rim, 240 g tubular tire) and my training wheels (500 g rim, 80 g tube, 500 g tire) was surprisingly small: If I put in 500 Watts from a standing start, after 100 m, I’d be up to a very high speed on both bikes. The lighter wheels would be half a foot ahead. Enough to win a race, but if I put out just 1% more power, I’d be faster on the heavier wheels. So if the racer who slept well on the heavier wheels will win against the racer on the lighter wheels who has been nervous about the race.

When factors are that small, you can safely say that they are “not very important”.

Even considering pulsating forces while pedaling, wheel inertia should not matter, provided the average speed is constant. The additional energy required to accelerate the wheel in the accelerating phase, is offset by the decreased energy required during the deceleration phase, where the wheel inertia works against the drag forces (rolling resistance, etc.). Basic physics.

That is basic physics, but it assumes that a rider will put out the same power on any bike. We’ve found in other studies that a rider’s power output depends on the bike they are riding. So if the short acceleration allows the rider to increase their power output because there is less resistance to the pedal stroke, then it could be beneficial.

There’s something a little strange with the Poertner data as it’s visualized above: the Y axis, which shows the coefficient of rolling resistance, has an inconsistent scale. Notice the tick marks and labels. Because of that, it’s hard to get a sense of the magnitude of the effect that’s being measured, particularly when comparing the different lines. Are the axis labels wrong, or does the scale actually change?

From the data above, it looks like increasing tire pressure improves performance on pavement, up to a point (for this tire and rider, about 100 psi for the yellow line), and then performance gets worse at higher pressures. I have been trying to run my tires at pressures that are as low as possible while still offering good handling. At the risk of overthinking this, the takeaway from the Poertner data seems to be that I should *increase* the tire pressure for pavement riding, and improve performance, up to the inflection point. I don’t know exactly where this inflection point is, but it’s likely to be above the as-low-as-you-can-go approach I have been using, no?

I suspect that the inconsistency you’re seeing in the Y-axis scale, is simply due to the way the software rounded the values on the axis. That is, the actual values could be, say, 0.0024, 0.0040, 0.0056, 0.0072, 0.0088, rounded to 0.002, 0.004, 0.007, 0.009

I’d just like to amend one statement in the above: “For riders, what matters most is how you can make your bike faster.” I realize that the bulk of your testing/research relies on power and performance, which provide reliable data, and for many riders, this statement is true; but for quite a few others, i’d say that what matters most is to make our bikes more comfortable, safer, more reliable – speed being a minor secondary benefit. Luckily enough, all those objectives should be well met with bigger tires run at a lower pressure (smoother, less fatiguing ride, easier to ride over debris, cracks, etc., fewer chances of flats…) so, well-done on all accounts, and kudos for bringing to the market better suited tires for real-life riding, not just on a big-ass steel drum.🙂

I am sorry that my comment could be misread. What I meant to say is that “For riders who care about performance, what matters most is how you can make your bike faster.” In other words, they don’t care about theory, but about speed on real roads. Whether higher pressures make your bike slower, or just not faster, doesn’t make a big difference. For anybody to run higher pressures, you’d want to see a significant increase in speed to put up with the discomfort, increased flat frequency, etc.

As you say, the beauty of wide, supple tires is that they are a “win-win-win-win” situation: They are faster, more comfortable, last longer and have fewer flats, compared to narrower tires at higher pressures.

Jan, how do suspension losses differ between a supple tire at low pressure, and a less-supple tire at slightly lower pressure? You often describe rigid casings as holding up the tire, so why can’t the stiffer tire simply be run at a lower pressure to achieve the same outcome as a supple tire at slightly higher pressure? With both of them deflated to their deflection points, aren’t we achieving the same outcome?

As far as suspension losses, you might get a similar outcome. Unless your tire is so stiff that it never deflects much.*

The big difference is that the stiffer tire at lower pressure will have much greater hysteretic losses – it flexes more, and it takes more energy to flex a given amount. So you lose much energy there.

* Many years ago, I rode an old 1950 Herse in Paris. I checked the Chinese tires using the “thumb” method, and they felt hard. I rode the bike for two hours in the informal race around Longchamps. (The racer-types were surprised that they couldn’t drop the guy on the grandpa bike.) The bike did feel sluggish and not very comfortable… When I got home, I checked the bike for the upcoming weekend ride with Ernest Csuka. The tire pressure was all of 17 psi, but with the stiff sidewalls, the tires were perfectly rideable and didn’t feel particularly forgiving! I’d love to try that bike with a set of Compass Babyshoe Pass Extralight tires!

Reblogged this on The Road to Revelation and commented:
Great post from BQ and Heine “Higher tire pressures don’t result in faster speeds – even on smooth pavement. Replicating results is a crucial part of science, which makes the new results an important milestone in the understanding of bicycle performance. No longer is it just Bicycle Quarterly talking about suspension losses and lower tire pressures – the science is becoming widely accepted.” (well, hopefully it is!) (Though there are plenty of Luddite-Thinkers out there…who still run 120, 130 psi on road tires… ugh) (The many False Narratives in cycling are enough to make one ill…

I get the suspension loss theory and ride the widest tires my frame clearance permits. However, riding on a rumble strip is not exactly a real world riding conditions test. No one purposely rides on rumble strips when encountered and suspension loss on rumble strips is quite obvious but not indicative of the real road conditions routinely encountered,

Of course, nobody rides on rumble strips. While the rumble strips are similar to cobblestones, few of us ride on cobblestones.

What we had to show was that suspension losses are significant. So we were looking for a place to show that riding on rough surfaces takes more energy than riding on smooth surfaces, with everything else being the same. The 290 Watts is sort of a maximum, but mostly, it shows that suspension losses can be very significant.

Without this test, we’d just be theorizing that suspension losses are important, but with no way to quantify them.

I have seen other studies where the goal was to rank tires by relative speed, as ‘product testers’ are prone to do. One used a tread plate drum (Velo News, I think), another using a weighted pendulum on a road surface (an HPV builder). The drum test also compared at various pressures. Reader comments often drew the conclusion that higher pressures were faster, though the authors did not. As long as the widths and pressures are similar, I wonder if the ranking still would hold true.

Any test that doesn’t consider the suspension losses will give erroneous results. When we started testing tires, we tried to replicate TOUR magazine’s tests, which were done on a steel drum. We found that some tires, especially the Michelin Pro Race 2 (this was in 2007) tested much worse on the road than on the drum. Generally, it seemed that harder rubber compounds worked very well on the drum, but actually made the tire slower on real roads.

On the steel drum, you at least have a shock absorber pushing the tire onto the drum. There will be some suspension losses in the shock absorber as it absorbs the vibrations, especially if you use a rough drum. A pendulum test will not measure suspension losses at all, so it’s of limited use.

Unless on the pendulum (or better, a bike cart) is sitting a person. If suspension losses are due to body tissues rubbing, a bike cart which is carrying a person, should have a higher resistance than if it’s carrying the equivalent weight as a rigid ballast.

I’m very interested in the methodology used, because trustworthy experiments in cycling seem very hard to create, especially as you move toward “real world” conditions. What was the methodology that you used for your research (e.g., how did you keep the test riders from knowing which wheel pressure they were riding with)? How did you control for changing conditions (riders, weather, etc.)? Were there peer reviewers? Where was Poertner’s paper published?

We published all our methodology and results in Bicycle Quarterly 29. The tests weren’t blind, because that is impossible: It’s easy to feel how much the bike vibrates with higher pressures. Since we measured power and speed, the rider’s influence was simply having to keep the bike at the speed we had selected. The lap times around the inner surface of the velodrome (chosen so we could ride on asphalt, not concrete) were within 1.5 seconds, so we did a good job on that. We always used the same rider and the same position. We checked in the University of Washington wind tunnel that our rider could assume the same position time and again. The error there was on the order of 1-2% (in wind resistance, not speed or power output).

We controlled for wind by choosing a totally calm day, and measuring wind speed frequently with a wind speed meter. We also chose a day with little temperature change, and we corrected for the effect based on a curve that we had established by testing the same tire at different temperatures. We also tested the same tire and pressure several times during the test day to make sure that conditions weren’t changing.

We did a rigorous statistical analysis to make sure we were seeing real differences between tires, and not just noise in the data. The paper was peer-reviewed by experts in the field: Jim Papadopoulos and Frank Berto.

I don’t think Poertner’s paper has been published yet. I hope his work will adhere to standard scientific procedures like ours, but unfortunately, that is rare in the bike world. Too many people just go and measure and report the results without showing that they are repeatable and statistically significant.

I’ve also been curious about the affects of temperature on tire performance. Living in the Midwest, we experience significant ranges in temperature and this dictates different tire pressure for my riding comfort and performance; single digit temperatures vs double digit temperatures (below freezing) plus the loss of psi from indoor storage to outside riding. Lots of other fun variables!

You don’t necessarily need to run a different pressure in colder temps (if riding on roads that are free of ice and snow). But you must be careful that the temperature hasn’t lowered the pressure. If you pumped up your tires when they were warm, once they get cold you will have lost pressure since the air got denser. With a fat bike and the low pressures I run there (6-15 psi), it can be quite noticeable.

On most bikes, the difference isn’t huge. I know that car tires, once they get hot from rotating on the road, will gain about 10% in pressure. For bicycles, that isn’t really that significant, so there is no need to add air to your tires when it gets cold. I don’t know about fatbikes, but I suspect that the same laws of physics apply – unless I am overlooking something.

I am convinced that a bike that is able to better follow road irregularities requires less energy and is faster, using supple lower pressure tires and flexible fork for smooth roads/gravel, or (on the other end of the range) a suspension fork for the very rough roads typical of mountain bikes.

However, I am not sure that this suspension losses are caused by vibrations in the body tissues. They could be trivially caused by micro-jumps due to road irregularities. In a jump, part of the energy is probably lost in the landing and not converted in forward motion. Even Josh Poertner seems to suggest a similar explanation.

However, apart from my hypothetical explanations, to establish if the losses are due to body tissue vibrations or micro-jumps, would be hard to do. Probably one should use a trike (able to travel for short distances with no one on board) with ballast and on a slope, and see if the results are the same, that is lower pressure leading to faster speeds. If the results are confirmed also for an unammend trike, then the reason for suspension losses is not body tissue vibrations but micro jumps.

In any case, be it one or the other, the end results don’t change: the more the road is rough, the more lower pressure become faster.

The U.S. Army showed in the 1960s with vibrating tank seats that a vibrating human body could consume up to 2000 Watts. The level of discomfort was directly proportional to the energy absorbed. It would be very surprising if a human body on a vibrating tank seat consumed that much power, but a human body on a vibrating bicycle consumed none!

On most irregularities, the bike doesn’t jump. If a tire deflects on a bump, it will absorb energy and then return that energy to forward motion as it “pushes off” the bump on the other side. There is a drawing of that mechanism in this post.

If it were like you said, then on a rough road you would have the same resistence than on a smooth road, since all of the absorbed energy would be returned (as per your reasoning). It’s a fact though, that even slight variation on road smoothness cause a variation in resistance. So, resistance does indeed depend on road smoothness.

We all agree that rough roads increase resistance, but we don’t agree where the energy is absorbed. If it really was just the bike jumping up and down, all the energy would have to be absorbed in the tires. 290 Watts is a lot of energy for the tires to absorb. The bike would be bouncing a lot more if you put that much energy into the tires in an up-and-down movement.

In reality, the energy is absorbed everywhere. I am sure some of it goes into the tires. (Even if they spring back, the deformation will cause hysteretic losses.) However, from the available science, it seems like the human body is the best candidate to absorb significant amounts of energy. It would be interesting to carry a large bag of rice or beans on the rack and see wether this increases the required power more than the same weight in a well-suspended solid object on the rack.

I read a bit on that research, and it’s indeed convincing. Now the only thing on which I’m not fully convinced is “planing”, all the other (wide tires, suspension losses, etc.) I’m certainly convinced.🙂

Thank you for the kind words. “Planing” will take a little more time until it’s generally accepted. It took almost 10 years for our work on tires to become accepted in the mainstream.

Our study of frame flex and performance actually is the most carefully controlled one we’ve done. It was a true double-blind test, and it clearly showed that power output of riders varies significantly with different bike frames and different flex characteristics.

I weigh 170lbs and ride Enve 3.4 clinchers with 23mm Conti GP4000s tires. They measure slightly more than 25mm on the wide Enve rims. Additionally, the roads I ride are paved but rough and full of potholes. Currently I ride 100 psi rear and 95 psi front. Thoughts?

Frank Berto’s tire pressure chart still is a good starting point. Note that the weights are per wheel, not for the entire bike/rider combination. Start with the values it recommends, then experiment to find what feels best.

What is the impact on potential flats. I am a believer where wider and less inflated tire pressures are concerned, but I am always wondering if the lower pressures will contribute to more flats, as a 3% increase in speed doesn’t matter much if there is a 10% increase in the likelihood of flatting. Has any work been done in this area?

Wider tires run at lower pressures, so they get fewer flats. They simply roll over debris that gets hammered into narrower tires that are inflated to harder pressures. Since switching to 42 mm tires, my flat frequency has been reduced by 75%.

I agree overall I experienced fewer flats since I moved to Babyshoe Pass extra light tires.

However, after a very annoying brevet where I got four flats in about a 10-mile stretch (road crews were cutting back blackberry brambles and the roads were strewn) I started using 2 oz of Orange Seal in each inner tube. No flats since with more than 1800km of riding.

I would love it if you could test the effect of adding tire sealant to tubes in supple tires. I can’t perceive any difference at all (other than no flats at all!) but I would be curious what BQ’s read on this is.

I am a keen cyclist from Australia, but I have also ridden in many other countries, mainly Italy, France, Spain Canada and USA.
Within the parameters of your test I believe they are correct and add important aspects to the debate – ‘more is not always better’..
Two extra aspects of tyre width to consider, especially when going fast.
1) At 30kph the bottom of the tyre is momentarily stationary as it touches the road. However, the top of the tyre is moving forward at 60kph, so frontal area and consequently wind resistance is a factor and the wider the tyre the greater the resistance. And the front tyre is right out there.
2) There is a complex interaction between the tyre and the road at point of contact. Difficult to explain, but best observed when riding on a wet road. Just watch the movement of water and spray around the front of the tyre as well as the back. One aspect is the rapid compression and expansion of air.
Both of these work against increasing tyre width and with narrow tyres pressure is so important to maintain tyre shape (especially on cornering) and avoiding pinch-flats.
Mike Perks

Our testing was done on real asphalt surfaces, with a rider on board, so wind and other resistances are part of the testing. We don’t just test rolling resistance, but the overall power required to pedal the bike at a certain speed. For our testing on the track, that speed was 28 km/h. If you go a lot faster, then it’s possible that the results will trend more toward narrower tires having an advantage.

We also tested 25 and 31 mm wide tires in the wind tunnel. The difference in wind resistance were too small to be statistically significant. We tested with a rider on the bike, pedaling. Tests that look at the wheel alone may show that wider tires have a larger frontal area and thus are less aerodynamic, but once you put the wheel on the bike, it’s right in front of the down tube and the spinning legs of the rider.

wow, your test determines that you need more power on a rougher surface than a smooth surface, the you go on to say get wide tires. There is no evidence in this report to recommend wide tires.

The truth:
“A common debate among cyclists centers on the issue of whether a wider tire has more or less rolling resistance at the same pressure. The constant pressure is proposed because it appears more scientific to eliminate this as a variable, but this is not realistic in practice. The short answer to this question is that, yes, a wider tire of similar construction will have lower rolling resistance than a narrower one at the same pressure. This fact is, however, of no practical value. If you are comparing two tires of similar construction, with the same load, and the same pressure, either the wider tire is overinflated, or the narrower tire is underinflated!”

This article is written by Journalist not necessarily with any background education (let alone a Stanford Education) whose very lively hood depends on continued advertising placements from the manufactures of the products they represent. You can choose who you place your confidence in.

Science changes with new evidence. Jobst Brandt was a firm believe that higher pressures made tires faster. We all believed this back then. But it’s simply not true on real roads with a real rider on the bike.

Two authors of the Bicycle Quarterly studies have Ph.Ds., and the studies all were peer-reviewed by other experts like Jim Papadopoulos and Frank Berto, whose qualifications are at least as high as Jobst Brandt’s. The evidence is clear: Higher pressures don’t make tires faster, and thus what Jobst wrote no longer is true. Both Sheldon Brown and Jobst Brandt are no longer with us. I am sure that if they were alive, they would have accepted the new science by now.

To read more about our studies and see some of the data, check out this blog post.

Finally, we don’t say that wider tires are faster on a smooth surface, just that they are no slower. And considering all the other advantages they have, it makes sense to use them. Especially if you don’t ride exclusively on smooth surfaces – why not choose a tire that is as fast on smooth surfaces and faster on rough ones – you’ll be faster overall.

There are other performance metrics rather than speed, as you noted in the original post where you describe not feeling as beaten up after riding wider tires. It’s difficult to understate this importance of this.

While speed is nice, gaining extra endurance/comfort from wider tires is a huge performance benefit. When I went from 28mm 700c to 42mm on 650b, I found that a 140 mile ride on 42mm felt about as fatiguing as a 100 mile ride on 28mm. My times were equal or modestly better consistently on wider tires. My relative comfort/endurance was massively better.

Scientifically quantifying something like that would be hard because it’s influenced by individual factors. But being materially less fatigued over the same distances with a modest speed benefit is huge performance win by itself.

I agree – fatigue is a huge factor. In the past, we used to think “Well, wider tires may be slower, but they don’t beat us up, so we’ll be happier and faster in the late stages of a long ride.” Now we know that the wide tires aren’t slower, so the reduced fatigue isn’t partially canceled by a lower speed – you get the full benefit.

These bicycles are going 75++mph which is obviously an extreme test of rolling & wind resistance. Of the few pictures that I’ve seen of these bikes, I’ve noticed that they are not based on skinny 700c wheels. Does anyone know the equipment considerations and trade-offs made for wheels/tires for these events?

I’m intrigued by this because the wheels/tires used in these events, from a traditional racing bike perspective, would be considered slow (also the bikes are not UCI legal). Is there knowledge that can be obtained from these bikes that can enable our equipment to be faster?

Maybe these records will be attempted with more supple tires in the future based on BQ testing?

You make an interesting point. I recall reading about the German HPV record trike, the Vector, in the late 1980s. Back then, they ran on ultra-narrow 700C tubulars pumped up to 200 psi. Like you, I’ve noticed that these machines now are a) using two wheels only to decrease their aerodynamic drag and b) run much wider tires to reduce their rolling resistance.

Of course, with a full fairing the wind resistance of the tires is less important, but you still have to consider the drag created by the wheels rotating inside the fairing. And yet, it seems that wider tires are faster for these machines, even at very high speeds.

In response to your advice, “Run the widest tire that fits your frame, at least within reason” brings me to the questions: where is the upper limit, and what is the optimal tire size? For example, I’d bet a 4″ fat bike tire is not faster on the road than a 32mm tire.

This could be simplified to, “what is the fastest tire size?” using your assumptions of 22 MPH and normal pavement.

We already know that a 25.5 mm wide tire is faster than a 23, which is faster than a 21. On a very smooth road, with a light rider and a bike that isn’t too stiff, a 28 and a 32 aren’t any faster, but also no slower. So you gain comfort and give up no speed. We haven’t tested wider tires on smooth pavement, but it appears that the plateau extends further – that is, wider tires also don’t slow you down. I suspect you are right – a 100 mm-wide tire may roll slower than a 42 mm tire.

However, I think the biggest constraints stem from the frame design – a 4″ fat bike tire doesn’t fit into a performance bike. Designing a drivetrain that has room for that wide a tire will compromise the rider’s ability to put out power… and less power will make you slower, that much we know for sure! That is the reason we made our Enduro Allroad tires 48-54 mm wide. That is about the widest you can fit on a bike with “road” cranks that have a low tread (Q factor).

Of course, once the pavement turns even a little bit rough, wider tires provide an advantage. How much depends on how rough…

Joshua Poertner’s data seems to go further, and indicate that even on very smooth pavement, wider tires may be faster. But we really have to see his study before we can draw definite conclusions.

I think we can reasonably assume that power to maintain speed is influenced by wider tires in two ways: reduced suspension losses and increased hysteresis losses. Obviously the suspension losses are a bigger factor when moving from 23 to 42mm so that is a net improvement. If going from 42 to 100mm, on smooth roads, I would assume that there’s very little improvement to be made in suspension losses, but hysteresis would increase enough to dominate and make it a net detriment to be on 100mm (ignoring the other impacts like rider power output from Q factors and aerodynamics). Of course how supple the tires are scales the impact of both hysteresis and suspension losses. So I imagine that threshold of too wide depends on the suppleness of the tires.

Regardless, within the realms of practicality to road and all road bikes, wider is better if it fits your bike.

You sum it up well, but without testing, we don’t know when the hysteretic losses start to overwhelm the gains from reducing suspension losses. It also will depend on the road surface – the rougher the road, the wider the “optimal” tire.

For reasons out of my control, I had to replace my titanium bike with its 35 mm Bon Jon Pass XLs with a Trek Domane SLR 6 Disc running 32 mm Grand Bois Cerfs. The ride of the Domane—which has a kind of small “suspension” front & rear—is unbelievable. Far better than any other endurance bike I’ve had. It irons out vibrations and big hits, and is more comfortable with its 32 mm tyres than the titanium bike with 35 mm. Washboard roads that were difficult are now easy to ride. I assume the carbon & suspension is “bending” like—or more than (?)—a thin wall steel frame. It certainly “bends” more than my titanium & carbon forked bike did. Is there an optimal ratio of frame “bend” to tyre width? Have you tried one of thee bikes and/or do you intend to test one? (35 mm tyres might just fit on it, which would make it even more comfortable.)

We found that comfort mostly comes from the fork (and the tires, obviously). A stiff fork will make the ride jarring. So if the Domane has a more comfortable fork, it’ll be way more pleasant to ride. Based on our testing, a steel fork with thin, small-diameter blades (like the Kaisei “Toei Special” blades we sell) has significantly more flex than a stiffer fork, whether it’s made from steel or carbon. (Carbon forks must be stiff, because if you flex carbon too much, it delaminates.) The difference also is very noticeable on the road.

On the rear, suspension can reduce the amplitude of some of the bigger hits, like tree roots or the expansion joints between concrete road panels. For casual riders with a very upright position, the comfort on the rear becomes more important, because all their weight rests on the saddle.